The present invention relates to information displays and, more particularly, to a novel liquid crystal display and method of driving the electrodes thereof to provide dark indicia upon a light background with essential invisibility of the electrode leads.
Liquid crystal displays are highly desirable due to their relatively low magnitude of power consumption. It is generally known that a desirable liquid crystal display will have a bright background upon which dark characters, symbols and other indicia are displayed. Typically, the indicia are formed of a multiplicity of segments, whereby a driving voltage is required, across the liquid crystal material of the display cell, over all of the background portion to render this portion in the clear, or highly light-transmissive, state. The indicia segments to be displayed in the light-transmissive condition must be driven, while the indicia segments to be displayed in the darkened condition must have the driving voltage removed therefrom. As each indicia-forming electrode segment must be directly connected to a driving voltage source by a conductive lead, the conductive leads on one of the pair of substantially parallel planar electrode surfaces tend to overlap background portions of the other electrode surface. When a particular segment is in the dark condition, and hence not receiving a driving voltage, the connective leads therefore, also being devoid of a driving voltage, causes the liquid cyrstal material associated therewith to be in the dark condition, whereby the segment leads are highly visible. This is especially true in the cholesteric-nematic or parallel-nematic types of liquid crystal displays, and whether or not the liquid crystal material is host to a dichroic dye. Hitherto, there has appeared to be no solution involving either electrode artwork or display drive variations, including any two-phase (0.degree. and 180.degree. phases, by use of an inverter), single frequency scheme which would provide switching of the active segment areas of the cell without also causing at least some of the leads thereto be become visible. Thus, it is highly desirable to provide a liquid crystal cell, having dark indicia upon a light background, in which the leads associated with the indicia-forming electrode areas are not visible during operation of the display.